1. Field of the Invention
The present invention relates to an alternator for vehicles that is mounted in a vehicle such as a passenger car or a motor truck.
2. Description of Related Art
In recent years, an engine main unit for vehicles has become lightweight in efforts to improve fuel economy as a countermeasure against environmental problems. Meanwhile, an engine driving torque has been increased in efforts to improve drivability. On the other hand, an alternator for vehicles that is driven by an engine is attached directly to the engine main unit with a bracket between them. Vibrations of the engine are likely to be conveyed to the alternator. The vibration resistance of the alternator must therefore be improved. Moreover, a vehicle engine speed at idle has decreased, and an engine room has been narrowed in order to ensure a large space for a vehicle compartment. Accordingly, the alternator for vehicles is requested to produce high power and to be compact. In addition, the heat resistance of the alternator against a rise in the temperature of the engine room is requested to improve. Moreover, the alternator for vehicles must generate little noise in compliance with a social demand for reduction in exterior noise or in pursuit of improvement in productivity derived from improvement in interior silence. Needless to say, the improvement in performance must be achieved at low cost.
U.S. Pat. No. 5,998,903 (JP-A-11-155270) discloses an alternator for vehicles that contributes to realization of a compact design, high power, and low noise. Herein, a stator winding is formed using a plurality of conductor segments. Conductor segments in different layers of different slots are coupled to each other in order to form a winding that offers a high space factor and a low resistance. Moreover, two three-phase windings are mounted in one stator. However, welding is required to couple segments. This poses a problem in that as the number of segments in slots increases, the number of welding machines, the number of welding steps, and the number of insulating steps increase. Moreover, as the number of segments in slots increases, the distance between welds is shortened. This poses a problem in that a short circuit is liable to occur between the welds.
U.S. Pat. No. 6,373,163 (Japan Patent No. 3155534) discloses an alternator for vehicle having a phase coil, e.g., X-phase, as shown in FIG. 16. The phase coil is provided by at least four wires each having a length corresponding to the circumferential length of a stator core. The wires are joined in order to thus create a coil assigned to one phase. For joining a plurality of wires, welding is required as shown in FIG. 16. The costs for a welding machine, a welding process, and an insulation process increase. Moreover, coil ends are elevated because of welds. This contradicts the trend to a compact design.
Accordingly, an object of the present invention is to provide an alternator for vehicles that is compact and low-cost and offers high power.
It is another object of the present invention to improve the heat resistance of the alternator by devising the shape of a coil end.
It is still another object of the present invention to prevent occurrence of a short circuit between coil ends despite an increase in the number of conductors to be held in slots.
It is yet another object of the present invention to reduce connections that require welding.
It is still yet another object of the present invention to provide an alternator capable of reducing noise by utilizing multiple sets of poly-phase windings while avoiding disadvantages resulted from complexity of the winding.
According to a first aspect of the present invention, one phase coil in a poly-phase winding is made of continuous wire that has only one crossing portion that links the same layers in different slots and two output portions. The other crossing portions of the phase coil links different layers in different slots. Consequently, a junction of coils is not created in a crossing portion at the coil end. This contributes to reduction in the cost of manufacture.